Developmental aspects of mutants and wild types of Neurospora crassa are being compared in studies designed to interrelate form and function. All of the obvious morphological features of the sexual reproductive apparatus have now provided examples of deviant development as the result of gene mutation. Electron microscopy is used to define the aberrant properties of membrane systems and spindle pole bodies in mutants that fail to delimit ascospores. The membranes are to be isolated and examined for possible differences in their protein components. The specificity or nonspecificity of biotin starvation is being examined in reference to the production of phenocopies that mimic mutants whose membrane systems are incompetent in the process of spore excision. The anatomical basis of deviations in perithecial development are under examination.